Abstract: The invention relates to spectrometer measuring heads (12) for analysing characteristic variables of liquid, pasty or solid substances for optical spectrometer systems. Said measuring heads are characterised, in particular, by their long-term stability, low maintenance and simple production. A rotationally mounted mirror (I) and at least one source of optical radiation (2) or a device for uncoupling optical radiation are arranged in a housing (6) in such a manner that the optical radiation is incident, by orientating the rotationally mounted mirror either on a reference body (3) in the housing or on the substance (14) that is to be analysed via a window (7) of the housing. The mirror is mechanically coupled to a drive (4) or a bending beam and as a flexing resonator in the housing.